1. Field of the Invention
This invention relates to a process for separating a compound from water in a mixture of the compound and water by azeotropic distillation in the presence of an entrainer.
2. Description of the Prior Art
Heretofore, for example, separation of acetic acid from water in the mixture has been effectively effected by azeotropic distillation in the presence of an entrainer, that is, the azeotropic mixture of water and the entrainer is distilled from the top of a fractionating column while dehydrated acetic acid or a concentrated acetic acid is withdrawn from the bottom. This method is disclosed in U.S. Pat. Nos. 1,917,391 and 2,050,234 and British Pat. No. 298,137. This azeotropic distillation has various advantages such as a high efficiency of separation, low reflux ratio and a reduced heat energy required for distillation and the like.
However, according to this azeotropic distillation, the gas-liquid composition distribution in the column is much more complicated than that in a usual distillation, and such distribution is easily changed even by a slight change in quantity, composition, and temperature of the feed, quantity of refluxed entrainer, reflux ratio of the aqueous phase and other operating conditions and therefore, a stable operation of a distillation column is very difficult. For example, a minor change in the operating condition results in adversely affecting the separation efficiency at the top of the column and contamination of a bottom product with the entrainer when a higher boiling entrainer is used. In a usual distillation, when such change in a gas-liquid composition distribution in a distillation column occurs, a stable operation can be carried out by controlling the operation conditions such as reflux ratio, heat energy supplied to a reboiler and the like. However, in case of azeotropic distillation, simple control of the quantity of reflux of the entrainer and heat supply to the reboiler are not sufficient to suppress a change in the gas-liquid composition distribution in the distillation column, in particular a change in the azeotropic zone, further in particular, a change in the lower region of said azeotropic zone where the content of the entrainer in the liquid composition varies to a great extent.